What is the size of your baby during the 4th week?

By the fourth week of pregnancy, your baby, now called an embryo, is about the size of a poppy seed, measuring approximately 1-2 millimeters in length. During this stage, the embryo is starting to develop basic structures, including the beginnings of the brain and spinal cord. It's a crucial time for early cell division and the formation of vital organs. Overall, while still tiny, significant growth and development are underway.